bnxt_open() can fail in this code path, especially on a VF when
it fails to reserve default rings:

bnxt_open()
  __bnxt_open_nic()
    bnxt_clear_int_mode()
    bnxt_init_dflt_ring_mode()

RX rings would be set to 0 when we hit this error path.

It is possible for a subsequent bnxt_open() call to potentially succeed
with a code path like this:

bnxt_open()
  bnxt_hwrm_if_change()
    bnxt_fw_init_one()
      bnxt_fw_init_one_p3()
        bnxt_set_dflt_rfs()
          bnxt_rfs_capable()
            bnxt_hwrm_reserve_rings()

On older chips, RFS is capable if we can reserve the number of vnics that
is equal to RX rings + 1.  But since RX rings is still set to 0 in this
code path, we may mistakenly think that RFS is supported for 0 RX rings.

Later, when the default RX rings are reserved and we try to enable
RFS, it would fail and cause bnxt_open() to fail unnecessarily.

We fix this in 2 places.  bnxt_rfs_capable() will always return false if
RX rings is not yet set.  bnxt_init_dflt_ring_mode() will call
bnxt_set_dflt_rfs() which will always clear the RFS flags if RFS is not
supported.

Fixes: 20d7d1c5 ("bnxt_en: reliably allocate IRQ table on reset to avoid crash")
Signed-off-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>